Introduction

The Proteomics Standards Initiative (PSI) aims to define community standards for data representation in proteomics to facilitate data comparison, exchange and verification. For detailed information on all PSI activities, please see PSI Home Page.

The PSI-MI interchange format and accompanying controlled vocabularies was originally designed by a consortium of molecular interaction data providers from both academia and industry, including BIND, DIP, IntAct, MINT, MIPS, GlaxoSmithKline, CellZome, Hybrigenics, Universities of Bielefeld, Bordeaux, Cambridge, and others. It is maintained, and kept fit for purpose by the Molecular Interaction workgroup of the HUPO PSI. Please contact us on psi-mi@ebi.ac.uk if you wish to become involved or have any questions.

Purpose of the PSI MI XML format

The PSI MI format is a data exchange format for molecular interactions. It is not a proposed database structure.

Directory structure

This document is in the root directory of the PSI-MI XML2.5 release. Subdirectories are

doc/Auto-generated documentation of the PSI-MI XML schema

src/Source code for schema and related software

data/Controlled vocabularies

tools/Data management tools

Release schedule

Level 3.0 will be published in 2016.

Level 2.5 was released 5 December 2005. It is the format most commonly supported by PSI-compliant databases and tools. It will continue to be supported by the MI workgroup after the publication of PSI-MI XML3.0.

Level 1.0 support was discontinued in 2007.

Changes from PSI-MI XML1.0 to 2.5

Changes in the PSI-MI XML format and controlled vocabularies from version 1.0 to 2.5 are documented in this page.

PSI-MI XML2.5 Maintenance releases

2.5.4

Minor change to header

2.5.3: Minor updates as a result of the PSI spring meeting in San Francisco, April 2006:

featuretype@id now mandatory. This was inadvertedly made non-mandatory with 2.5.2.

Optional attribute parameter/uncertainty added.

Added participant/parameterList and participant/attributeList to allow more complex modelling of participants.

Deleted XML constraints on entry level. They were not working due to syntax errors, and few XML validators can check them. This validation level will be performed by the PSI XML validator in the future.

2.5.2: There were some inconsistencies in the naming of complex types in 2.5.1. These have been fixed. This has no impact on the XML data files. The only impact for users is a facilitation if they use code generators. Concrete changes:

complex type interactorType to interactorElementType

complex type interactionType to interactionElementType

complex type featureType to featureElementType

featureType@id has been moved into the complex type featureElementType and typed as xs:int

2.5.1: At the PSI meeting in Geneva, September 2005, it was discussed that participant/experimentalFormList/experimentalForm should have the possibility to assign a position, e.g. to describe an n-terminal protein modification in an experiment. It was decided to implement this using the existing featureType. The controlled vocabulary has been updated accordingly, but the change in the XML schema was not implemented. This required the maintenance release 2.5.1, with the following changes:

Detailed Documentation

Use of external controlled vocabularies

Where possible, external controlled vocabularies are referenced from PSI MI. External controlled vocabularies are used in two forms:

Open controlled vocabularies: We think that no existing controlled vocabulary provides all necessary terms for the given attribute in the PSI MI format. In this case, it is up to the data provider to choose a controlled vocabulary, or to provide a free text string if no appropriate controlled vocabulary exists.

Closed controlled vocabularies: We think that there is a controlled vocabulary which appropriately covers all necessary terms for the given attribute. In this case, only terms from the defined vocabulary should be used.

Data

The closed controlled vocabularies referenced by PSI MI are listed in the table below. All vocabularies are contained in a files in OBO flat file format: psi-mi25.obo. They can be browsed at the EBI OLS (Open Lookup Service). The correctness of references to external controlled vocabularies is currently not enforced by the PSI MI schema. It is the responsibility of the data provider to ensure that only existing terms at an up-to-date data source are referenced.

Obsolete terms

The OBO format has a special class “obsolete”, to which all obsolete PSI MI terms are assigned.

Mapping from OBO to MIF25 format

We recommend the following mapping from the file psi-mi25.obo to PSI MI 2.5 XML files:

OBO format element

PSI MI 2.5 XML file element

id

cvType/xref/primaryRef/id

name

cvType/names/fullName

exact_synonym

cvType/names/shortLabel

synonym

cvType/names/alias

Feedback

Because we are following a leveled approach, we are interested in knowing what the community wishes to be included in the next level. If you have a use case not covered by the current schema or controlled vocabulary terms, please contact us at psi-mi@ebi.ac.uk.

Data submission

We strongly support and encourage data deposition supporting published journal articles in public databases of the IMEx consortium. Please see the IMEx deposition page for contact details and deposition options.